These teachings relates generally to control of power supplies and similar devices.
Power supplies and in particular buck regulators are an important parts of today's technology. These devices consist of mainly two main parts, the power electronics and the controller. The controller functions to operate the power electronics in a manner that satisfies the system requirements of the load. Both the power electronics section and the controller need to be designed to meet the demanding objectives of the electrical specifications and cost. Due to the reduction in cost of digital electronics as popularized by Moore's law, a recent trend is the use of digital electronics for the controller.
Key desired features of an effective controller are: fast settling time, low DC error, adjustable output impedance, current limit, and stability.
There is a need for a high performance digital compensator controller with the above listed desired features.
Digital compensators are typically implemented as a PID or PID with additional filtering. These are typically digital implementations of older analog designs.
There are three common methods used for current sensing. The first method measures the voltage drop across one or more of the power FETs and uses the on resistance of power FET to calculate inductor current. This method has significant limitations. First, the on resistance of the power FET has a large tolerance and as temperature dependence. Second voltage across the FETs are very small and is difficult to measure accurately.
FIG. 2 illustrates the second method of a sense resistor in series with the inductor. The voltage across sense resistor is measured and the current is then determined. The limitation with this method is the requirement for an external power resistor in series with the inductor. This resistor lowers the supply efficiency and increases cost. To improve efficiency, the resistor value can be lowered, but this complicates measurements due to noise.
As shown in FIG. 3, the third method uses an external RC network to model the inductor and its series equivalent resistance, Rdc. One difficulty of this method is that the series resistance of the inductor is temperature dependent and may be unknown. In addition, other practical limitations occur due to the fast switching of the FET outputs and its noise.
All of the above methods suffer from noise sensitivity and, in two of the cases, parameter uncertainty. Also, what is desired for compensation is not the actual inductor current but the inductor current average over one PWM cycle. In continuous conduction, inductor current has a triangular like waveform due to the pulse width modulated drive signal from the power FETs. None of these methods provide the actual average inductor current.
There is a need for a method that reduces component cost, reduces noise sensitivity, is parametric stable and provides the average inductor current over one PWM cycle.